Therapeutic agents have been implanted into patients for treatment of chronic conditions, deficiencies and disease. In one form of treatment, microcapsules containing cells (or cell clusters) for producing such therapeutic agents, have been used. Specifically, pancreatic islet cell grafts have been performed by implantation either freely into the peritoneal cavity or into an epiploic flap pedicle. (Cugnenc, P. H., et al., Chirurgie 1990, 116(6) p.268-74, and Altman, J. J., Horm. Metab. Res. Suppl. 1990, 25 p.136-7.) Microcapsules containing other cells have been implanted in various areas of the body. One problem with known techniques is that there is no effective way to retrieve the encapsulated cells. In certain instances, it would be desirable to replace such cell capsules because of (a) possible expiration or failure of the cells, (b) a need to change the therapeutic approach or modify the dosage levels, (c) catastrophic failure, or (d) allergic reaction. When using microcapsules, a large number (e.g. hundreds or thousands) are normally employed for dispersion within the individual thereby effectively preventing retrieval.
Another approach which has been suggested is the loading of tissue fragments of insulinomas in permselective tubular membranes which are implanted. (Altman, J. J., Diabetes June 1986, 35(6) p.625-33.) Altman reports that the insulinoma tissue retrieved after implantation showed functionally active endocrine cells and no evidence of graft rejection. However, this is not the optimum environment for long term grafts because the cells are not in close proximity to well-vascularized tissue. Also, the unencapsulated cells do not have optimal diffusional characteristics.
In view of the foregoing, there is a need for implantation of encapsulated or unencapsulated cells into a patient providing optimum conditions for long term cell viability and which permits the complete retrieval of such cells.